Controlled atmosphere generating equipment

ABSTRACT

An apparatus to produce a low oxygen containing gas in which exhaust gases from an engine are cooled by passing them through a manifold cooler. Harmful gases are removed by passing the exhaust gases through a catalytic converter for removal of NOX. Air in injected and the exhaust gas passed through a further catalytic converter for removal of CO. The exhaust gases are then cooled by passing them through an air to gas heat exchanger, and a series of water-cooled heat exchangers which are water-cooled and the resulting condensate removed by condensate drain. The water coolant is supplied by a closed circuit radiator system. The exhaust gases are then passed through a condensate screen and two filter beds for removal of moisture which may be regenerated by passing warm air derived from the air to gas heat exchanger through them when not in use. The operation of the system may be regulated by a fuel management system which includes an oxygen sensor.

FIELD OF THE INVENTION

The present invention relates to apparatus for the production of a lowoxygen containing gas.

BACKGROUND OF THE INVENTION

Whilst the following description of the apparatus for generating acontrolled atmosphere particularly refers to its application to grainsand foodstuffs, the equipment has application to other areas where acontrolled atmosphere is desired. For example, tobacco, feed stock,rice, fruit and metallurgical processing.

Storage of grains and foodstuffs has for a long time presented problemsrelating to maintaining the integrity of the grains and foodstuffs andreducing any degradation caused by foreign organisms. Studies of thedegradation in the storage of grains and foodstuffs over a prolongedperiod have been carried out by the Commonwealth Scientific andIndustrial Research Organisation ("C.S.I.R.O."). In particular anentomological study of the effects of foreign growths upon wheat andother grains has been reported. According to these reports, wheat andother grains are subject to attack from organisms which can causespoilage of the stored grain. Further, these studies have also revealedthat the quality of grains may degenerate over an extended period due tothe effects of oxygen on the grains.

The studies of C.S.I.R.O. have also shown that storage of grain, inparticular wheat, in an inert atmosphere, under conditions of reducedmoisture and in particular minimized oxygen, results in foreignorganisms becoming dormant and ultimately dying. It has also beenreported that such inert atmosphere does not interfere with thenutritional value of the grain thus enabling it to be stored safely forprolonged periods. It has also been shown that moulding may be reducedand the germination level retained in such conditions.

STATEMENT OF THE INVENTION

Accordingly, it is an object of the present invention to provide anapparatus and method for generating a controlled atmosphere low inoxygen content in a storage container.

According to a first embodiment of the invention an apparatus isprovided for producing an exhaust gas having a low oxygen contentcomprising:

(i) means to combust a mixture of air and fuel to produce an exhaust gascontaining N₂, CO, NOX, inert gases and small amounts of uncombusted O₂;

(ii) at least one catalytic convertor means to substantially reduce theNOX and/or CO content in the exhaust gas;

(iii) at least one heat exchange means to substantially reduce thetemperature of the exhaust gas issuing from the at least one catalyticconvertor; and

(iv) an absorption system through which the exhaust gas passes tosubstantially reduce the moisture of the exhaust gas.

According to a second embodiment of the invention a method is providedfor producing an exhaust gas having a low oxygen content comprising thesteps of:

(i) combusting a mixture air and fuel to produce an exhaust gascontaining N₂, CO, NOX, inert gases and small amounts of uncombusted O₂;

(ii) passing the exhaust gas through at least one catalytic convertormeans to substantially reduce the NOX and/or CO content in the exhaustgas;

(iii) passing the exhaust gas through a heat exchanger to reduce thetemperature of the exhaust gas issuing from the at least one catalyticconverter; and

(iv) passing the exhaust gas through an absorption system tosubstantially reduce the moisture content of the exhaust gas.

PREFERRED EMBODIMENTS

Preferably, the means to combust a mixture of air and fuel is aninternal combustion engine, pulse jet engine or gas turbine engine. Morepreferably the means should be capable of combusting propane.

In another preferred embodiment the apparatus additionally comprises atleast one additional heat exchange means between the means to combust amixture of air and fuel, and the at least one catalytic converter means,to reduce the temperature of the exhaust gas. For example, theadditional heat exchange means is a water-cooled manifold. Otherexamples are a water to gas heat exchanger and an air to gas heatexchanger.

In another preferred embodiment the catalytic converter means comprises:

(i) a first catalytic converter section to substantially reduce NOX inthe exhaust gas;

(ii) a second catalytic converter section to substantially reduce CO inthe exhaust gas; and

(iii) air injection means to introduce air into between the first andsecond catalytic converter section to enhance the reduction of CO in theexhaust gas.

Typically the first catalytic converter section consists of twocatalytic chambers.

The air injection means may include an air line from a modified petrolvacuum pump and a flow meter to monitor the volume of air injectedbetween the first and second catalytic section.

In further preferred embodiments of the invention the absorption systemcan take on a number of arrangements. For example, it may include meansto collect and/or remove moisture from the exhaust gas. Typical of theseis a condensate knock-out means, and a condensate drain tank. If acondensate drain tank is selected it may include a submerged automaticdrain which maintains a liquid seal with the atmosphere.

Alternatively or additionally the means to collect and/or remove themoisture from the exhaust gas may be a desiccant, e.g. wheat. In thisarrangement the system may comprise:

(i) a first absorbent chamber containing a desiccant;

(ii) a second absorbent chamber containing a desiccant;

(iii) means to direct the exhaust gas to the first absorbent chamberuntil the first absorbent chamber has absorbed a predetermined amount ofmoisture from the exhaust gas;

(iv) means to thereafter direct the exhaust gas to the second absorbentchamber until the second absorbent chamber has absorbed a predeterminedamount of moisture; and

(v) means to regenerate the desiccant in the first or second absorbentchamber with warm regenerative air to reduce the moisture content of thedesiccant.

Preferably the warm regenerative air is supplied from the additionalheat exchanger means.

To enhance the operation of the apparatus it is desirable to include:

(i) sensor means to sense and measure oxygen in the exhaust gas issuingfrom the absorption system; and

(ii) means to control and adjust the mixture of air and fuel, inresponse to the sensor means.

Typically the apparatus produces an exhaust gas containing nitrogen(typically greater than 80%), carbon dioxide (typically 10%-14%depending on fuel composition) and steam with only trace amounts ofoxygen (e.g. less than 0.5% oxygen), less than 5 ppm NOX (oxides ofnitrogen) and less than 50 ppm carbon monoxide.

The issuing exhaust gases should preferably not increase the moisturecontent of the container into which it is fed and therefore those gasesare preferably treated, as indicated, in the additional heat exchangerso as to remove substantially all the moisture content.

The removal of moisture from the exhaust gases (and the controlling ofgas quality) may be conveniently achieved by passing the exhaust gasfrom the engine via a water-cooled manifold to a catalytic converter. Asthe temperature of the gases issuing from the converter is very high, itis preferred to pass these through water to gas or air to gas heatexchangers. Cooling water may be supplied to these heat exchangers fromthe circulation of water achieved by a conventional water pump through acooling radiator. Thus, a closed circuit heat exchanger can be providedto cool the exhaust gases from the engine. Of course, a closed circuitis not essential and the heat exchange medium could be removed as waste.

As indicated, preferably, the catalytic conversion is carried out usingtwo catalyst sections. The first catalyst section consists of twocatalytic chambers. In this embodiment, after the first catalystsection, air is injected at a controlled rate prior to the secondcatalyst section. The air injection is taken by an air line off amodified petrol vacuum pump designed to inject low pressure air, via aflowmeter, to an injection point between the first and second catalystsections.

The amounts of low pressure injection air may need variable control tocover the range of engine revolutions envisaged for the purge and top-upphases of the gas generator. This double catalyst section, withintermediate low pressure controlled air injection system, has beenfound to control the harmful exhaust gases NOX and CO to less than therequired maximum allowable parts per million limits. It has been founddesirable in the first catalyst section to use two catalytic chambers toensure that NOX gas is controlled at acceptable levels.

The cooling of the exhaust gases generates condensate. This is drainedoff continuously into a condensate drain tank.

As also previously indicated to further reduce the moisture content ofthe exhaust gases, it is preferred to pass the gases through a waterabsorption system. Specifically for wheat storage systems the waterabsorption system will consist of wheat filters, using wheat as theabsorbent, or alternative desiccants if necessary. Wheat has been foundto be most successful not only as a moisture absorber but also as afinal remover of other pollutants prior to injection into the wheatstorage system.

A tandem wheat regeneration system may also be incorporated using an airto gas heat exchanger to give warm regenerative air to the off lineabsorber. This changeover system is designed to ensure that both filtersare maintained in effective working condition. Filter beds are alsodried out using the regeneration system prior to machine shut down.Special two way rubber sealed, spring loaded flap valves have beenspecifically designed to be hydraulically operated on this loose linkchangeover system, as they were not commercially available.

It has also been proved that the absorber-regenerator system needs acounter flow arrangement of gas in at the bottom, whilst hot airregeneration inlet is at the top of the beds.

When the controlled atmosphere machine is used on other storage mediums,alternative desiccants may be used.

Additional condensate knock-out facilities have been built into thefilter cans. Condensate so removed also drains back to the condensatetank. The condensate tank includes a submerged automatic drain valve tomaintain a liquid seal to the atmosphere.

In a further preferred embodiment of the invention, where the amount ofoxygen in the exhaust gas is to be minimized, close control of thecombustion of the fuel (e.g. liquid petroleum gas or LPG) and air isdesired. As will be readily appreciated, combustion of LPG to oxygen inproper stoichiometric ratio will theoretically achieve a minimum amountof oxygen and unburnt hydrocarbon and other products of partialcombustion issuing in the exhaust gases. To achieve this close controlit is desirable to locate an oxygen sensor in the exhaust stream andprovide electronic circuitry connected to this and to an air/fuel ratiocontroller to adjust the air/fuel ratio to minimise the oxygen contentin that exhaust stream. Oxygen sensors are well known and readilyavailable. However, it has been necessary to utilize an air/fuel ratiocontroller which is simple and adapted to quickly respond to changes inthe sensed oxygen content in the exhaust stream. One such suitableair/fuel ratio controller is sold under the trade mark IMPCO.

Air/fuel ratio control is carried out by extremely fine control on fuelin conjunction with pre-set engine revs and air volume. A low pressureair injection system is taken off the regenerative air blower line, andinjected at constant pressure and volume for any pre-set engine speed.This injection system gives the engine consistent conditions forstoichiometric combustion, irrespective of continual changes ofatmospheric conditions, barometric pressure, and wind effects.

Controlled combustion air then allows for controlled fuel injection. Thefine fuel injection is effected mechanically by the motorised movementof a specifically tapered needle inside an orifice.

Noise levels from the machine are to be kept at a minimum. In additionto normal sound attenuation procedures, wherever possible all noisegenerating items have been designed to direct noise vertically up fromthe gap generator.

DESCRIPTION OF THE INVENTION

The present invention will now be further described with reference tothe accompanying drawings in which:

FIG. 1 is a flow diagram of an apparatus according to the invention.

As shown, an engine 1 is provided, which may be an internal combustionengine or a pulse generator, small turbine or other combustion device.

The engine supplies exhaust gases and a source of power, eithermechanical, electrical or hydraulic, to drive fans, blowers andcompressors, and the electrical requirements of the engine (not shown).

Exhaust gases issue from the engine and pass via a manifold cooler 2 tothe catalyst package.

The catalyst package has two catalytic converters 3 and 5. Air may beinjected via an air injection system 4 between the two catalysts tocontrol the products of combustion within satisfactory limits.

The exhaust gases then pass through a series of heat exchangers. Thefirst is an air to gas heat exchanger 6 which provides an initialcooling to the exhaust gases. Further cooling is achieved by passing theexhaust gases subsequently through water-cooled heat exchangers 7, 9 and10. The water coolant is supplied to heat exchangers 7, 9 and 10 from aclosed circuit radiator system 14. Interposed between heat exchanger 7and heat exchanger 9 is a condensate drain 8. Condensate drain 8 removescondensate during the gas cooling flow path, reducing the moisturecontent of the exhaust gases. The cooled exhaust gases issuing from heatexchanger 9 enter another heat exchanger 10 to further reduce thetemperature of the exhaust gases.

Finally, the exhaust gases are passed into a condensate knock-out screen11 built into the filter cans and through two filter beds 12 and 13. Thefilter beds are wheat filters which reduce the moisture content of theexhaust gases. These filter beds may be regenerated by passing warm airderived from the air to gas heat exchanger 6 through them when not inuse.

The system's operation is regulated by a fuel management system 15. Thissystem 15 includes an oxygen sensor located in the issuing gas from theapparatus and interacts with the air/fuel controller to regulate theair/fuel ratio in the combustion chamber of the engine to minimise theoxygen content of the exhaust stream.

The apparatus of the present invention is relatively simple and iscapable of maintaining the required atmosphere for an extended length oftime. Typically the exhaust gas which is fed to a foodstuff containingarea comprises the following composition:

86% nitrogen

12.8% carbon dioxide

1.1% argon

0.1% oxygen

<5 ppm NOX

<50 ppm carbon monoxide

The close control of the air to fuel mixture enables a constant steadyload to be applied to the engine.

The use of this apparatus which runs on relatively cheap fuel avoids theneed to introduce chemicals to treat stored foodstuff material and hasbeen found to provide an exhaust which has a very low oxygen contentthereby acting as an insecticide to the foodstuff by killing pestinfestation such as Cryptoleses ferrugineus.

The apparatus is adapted to be transportable and self-contained thoughcan be readily integrated with other power sources.

EXAMPLE

14 kg/hr of propane fuel was burnt in a modified LPG fixed sparkignition internal combustion engine. 170 m³ /hr of exhaust gas wasproduced which comprised <0.5% oxygen, ppm NOX, unburnt fuel, CO andinert gases. The temperature of the gas was 300-400 degrees Celsius.

The exhaust gas was cooled by 50-100 degrees Celsius by passing througha custom made water-cooled manifold similar in design to a marine enginewater-cooled manifold.

The gas which was at least 300 degrees Celsius was then passed throughtwo fuel rich catalytic converters comprising Nissan Part No.20802-J7100 for removal of NOX through the following typical reaction:

    2NOX+2XCO=2XCO.sub.2 +N.sub.2

Sufficient air was injected into the exhaust gas at a low controlledpressure prior to entering a platinum based catalyst for removal of COthrough the following typical reactions:

    2CO+O.sub.2 =2CO.sub.2

    C.sub.3 H.sub.3 +50.sub.2 =3CO.sub.2 +4H.sub.2 O

The temperature of the issuing gas was 300 degrees Celsius.

The temperature of the exhaust gas was reduced from 300 degrees Celsiusto 45 degrees Celsius by passing the exhaust gas through a series ofwater to gas heat exchangers.

The cooling water was supplied to the water to gas heat exchangers froman air to water radiator in a closed loop. The radiator configurationwas a twin bank vertical radiator module.

The radiator air was supplied by a hydraulically driven axial fanmounted above the radiator to create an induced draft with exhaust airvertically upwards resulting in fan noise being directed verticallyupwards.

Up to 10 l/hr of condensate generated by the reduction of temperature inthe exhaust gas was drained off via condensate drain tanks.

Much of the remaining condensate and pollutants was absorbed using atandem wheat regeneration system with wheat as the absorbent. Themoisture contents before and after were not recorded. The conditions ofabsorption were a gas flow just above ambient temperature and pressure.An air to gas heat exchanger was incorporated to give warm regenerativeair to the off line absorber. This regeneration system was designed toensure that both filters were maintained in effective working condition.Filter beds were also dried out using the regeneration system prior tothe machine being shut down. Special two-way rubber-sealed spring-loadedflap valves were specifically designed to be hydraulically operated onthe loose link regenerator or changeover system. The changeover systemrequired a counterflow arrangement of gas at the bottom whilst the hotair regeneration was at the top of the filter beds.

The claims defining the invention are as follows:

We claim:
 1. An apparatus for producing an exhaust gas having a lowoxygen content comprising:(i) means to combust a mixture of air and fuelto produce an exhaust gas containing N₂, CO, NOX and small amounts ofuncombusted O₂ ; (ii) at least one catalytic converter means tosubstantially reduce the NOX and/or CO content in the exhaust gas; (iii)at least one heat exchange means to substantially reduce the temperatureof the exhaust gas issuing from the at least one catalytic convertermeans; (iv) an absorption system through which the exhaust gas passes tosubstantially reduce moisture content of the exhaust gas, saidabsorption system comprising a regeneratable desiccant; and (v) meansfor subjecting the desiccant to heat energy from a stream of air toregenerate the desiccant to reduce the moisture content of thedesiccant, the heat energy from the stream of air being the sole form ofenergy employed for regenerating the desiccant, and wherein followingcombustion of the air and fuel mixture, the exhaust gas passes through,in turn, the catalytic converter means, the heat exchange means and theabsorption system.
 2. The apparatus according to claim 1 wherein themeans to combust a mixture of air and fuel is an internal combustionengine, pulse jet engine or gas turbine engine.
 3. An apparatusaccording to claim 1 additionally comprising at least one additionalheat exchange means between the means to combust a mixture of air andfuel and the at least one catalytic converter means, to reduce thetemperature of the exhaust gas.
 4. An apparatus according to claim 3wherein the at least one additional heat exchange means is awater-cooled manifold.
 5. An apparatus according to claim 3 wherein theat least one additional heat exchange means comprises a water to gasheat exchanger or an air to gas heat exchanger.
 6. An apparatusaccording to claim 1 wherein the at least one catalytic converter meanscomprises:(i) a first catalytic converter section to substantiallyreduce NOX in the exhaust gas; (ii) a second catalytic converter sectionto substantially reduce CO in the exhaust gas; and (iii) air injectionmeans to introduce air into and between the first and second catalyticconverter sections to enhance the reduction of CO in the exhaust gas. 7.An apparatus according to claim 6 wherein the first catalytic convertersection consists of two catalytic chambers.
 8. An apparatus according toclaim 6 wherein the air injection means includes a modified petrolvacuum pump and an air line connected thereto.
 9. An apparatus accordingto claim 8 wherein the air injection means further includes a flow meterto monitor the volume of air injected between the first and secondcatalytic converter sections.
 10. An apparatus according to claim 1wherein the at least one heat exchange means is an air to gas heatexchanger or a water to gas heat exchanger.
 11. An apparatus accordingto claim 10 wherein the at least one heat exchange means is the water togas heat exchanger supplied with water cooled by circulation through acooling radiator.
 12. An apparatus according to claim 1 wherein theabsorption system further comprises a condensate screen.
 13. Theapparatus according to claim 1 wherein the absorption system furthercomprises means to collect and/or remove moisture from the exhaust gas.14. An apparatus according to claim 13 wherein the means to collectand/or remove moisture comprises a condensate drain tank.
 15. Anapparatus according to claim 14 wherein the condensate drain tankincludes a submerged automatic drain which maintains a liquid seal withthe atmosphere.
 16. An apparatus according to claim 1 wherein theabsorption system comprises:(i) a first absorbent chamber containing adesiccant; (ii) a second absorbent chamber containing a desiccant; (iii)means to direct the exhaust gas to the first absorbent chamber until thefirst absorbent chamber has absorbed a predetermined amount of moisturefrom the exhaust gas; (iv) means to thereafter direct the exhaust gas tothe second absorbent chamber until the second absorbent chamber hasabsorbed a predetermined amount of moisture; and (v) means to direct thestream of air to the first or second absorbent chamber to regenerate thedesiccant.
 17. An apparatus according to claim 16 wherein the desiccantis wheat.
 18. An apparatus according to claim 17 in which the means forsubjecting the desiccant to heat energy from the stream of air toregenerate the desiccant receives the heat energy from the at least oneheat exchange means.
 19. An apparatus according to claim 1 furthercomprising:(i) sensor means to sense and measure oxygen in the exhaustgas issuing from the absorption system; and (ii) means to control andadjust the mixture of air and fuel in response to the sensor means. 20.An apparatus according to claim 1, wherein the at least one heatexchange means is a water to gas heat exchanger.
 21. An apparatusaccording to claim 1, wherein the means for subjecting the desiccant toheat energy from the stream of air to regenerate the desiccant receivesthe heat energy from the at least one heat exchange means.
 22. Anapparatus according to claim 1, wherein the desiccant is a grainmaterial.
 23. An apparatus according to claim 22 wherein the desiccantis wheat.
 24. A method for producing an exhaust gas having a low oxygencontent comprising the steps of:(i) combusting a mixture of air and fuelto produce an exhaust gas containing N₂, CO, NOX and small amounts ofuncombusted O₂ ; (ii) passing the exhaust gas through at least onecatalytic converter means to substantially reduce the NOX and/or COcontent in the exhaust gas; (iii) passing the exhaust gas from step (ii)through a heat exchanger to reduce the temperature of the exhaust gasissuing from the at least one catalytic converter means; (iv) passingthe exhaust gas from step (iii) through an absorption system comprisinga regeneratable desiccant to substantially reduce moisture content ofthe exhaust gas; and (v) regenerating the desiccant in the absorptionsystem by subjecting the desiccant to heat energy from a stream of air,the heat energy from the stream of air being the sole form of energyemployed for regenerating the desiccant.
 25. A method according to claim24 wherein the mixture of air and fuel in step (i) is the mixture of airand propane.
 26. A method according to claim 24 comprising theadditional step of passing the exhaust gas from step (i) through anadditional heat exchanger to reduce the temperature of exhaust gas priorto passing the exhaust gas into step (ii).
 27. A method according toclaim 24 wherein step (ii) includes:(a) passing the exhaust gas througha first catalytic converter section to substantially reduce NOX in theexhaust gas; (b) injecting air into the exhaust gas issuing from step(a); and (c) passing the exhaust gas and air mixture into a secondcatalytic converter section to substantially reduce CO in the exhaustgas.
 28. A method according to claim 27 wherein the air injected intothe exhaust gas in step (b) is metered according to predeterminedconditions to allow the substantial reduction in CO in step (c)thereafter.
 29. A method according to claim 24 wherein step (iv)includes the steps of:(a) passing the exhaust gas from step (iii) into afirst absorbent chamber containing a desiccant until the desiccant hasabsorbed a predetermined amount of moisture from the exhaust gas; and(b) redirecting the exhaust gas from step (iii) thereafter to pass intoa second absorbent chamber containing a desiccant until the desiccanthas absorbed a predetermined amount of moisture from the exhaust gasfrom step (iii);and wherein step (v) includes the step of alternativelyregenerating the respective desiccant of the first and second absorbentchambers when not in use with the regenerative stream of air to reducethe moisture content of the respective desiccant.
 30. A method accordingto claim 29 wherein the heat energy from the regenerative stream of airis produced by heat exchange in the heat exchanger of step (iii).
 31. Amethod according to claim 24, wherein the stream of air for regenerationof the desiccant is at a temperature of less than 100° C.
 32. A methodaccording to claim 24, wherein the desiccant is a grain material.
 33. Amethod according to claim 32, wherein the desiccant is wheat.